Head suspensions are well known and commonly used with dynamic storage devices or disk drives with rigid disks. The head suspension is a component within the disk drive which positions a read/write head over the desired position on the storage media where information is to be retrieved or transferred. The head suspension for a rigid disk drive typically includes a load beam supporting a flexure to which a head slider having a read/write head is mounted. The head slider "flys" on an air bearing generated by the spinning rigid disk. The flexure allows pitch and roll motion of the head slider and its read/write head as they move over the data tracks of the rigid disk. Head suspensions are usually connected to either a rotary or linear actuator arm for moving the head suspension and head slider over the spinning disk.
With the advent of more powerful computers and the rapid growth in the personal computer market it has become increasingly more important to enable the user to access data from storage devices with increased speed and accuracy. Also, the industry is producing increasingly smaller disks having increasingly higher information density.
Because of this need to reduce access times to enable rapid retrieval of data from higher density drives, it has become increasingly more important to reduce undesirable levels of vibration of components within the rigid disk drive. In relation to this, an important consideration in the design of head suspensions is resonance characteristics. Resonance vibrations of drive components can cause instability of the head suspension and other components in a rigid disk drive. Resonance vibrations may also delay the transfer of data because the data cannot be confidently transferred until the amplitude of the vibrations have substantially decayed.
Of particular importance are the first and second torsion resonance modes and lateral bending (or sway) resonance modes of vibration. These resonance modes can result in lateral movement of the head slider at the end of the head suspension and are dependent on cross-sectional properties along the length of the load beam. Torsion modes sometimes produce a mode shape in which the tip of the resonating head suspension moves in a circular fashion. However, since the head slider is maintained in a direction perpendicular to the plane of the disk surface by the stiffness of the load beam acting against the air bearing, lateral motion of the rotation is seen at the head slider. The sway mode is primarily lateral motion.
Resonance problems can be controlled either by designing the head suspension so that resonance frequencies are outside the range of frequencies normally encountered in the storage device or by limiting gain of resonance frequencies. One way to limit gain is by using damping techniques. The use of dampers on head suspensions to decrease the amplitude or gain of resonance vibrations is generally known and described in U.S. Pat. No. 5,187,625 issued to Blaeser et al. on Feb. 16, 1993 ("Blaeser") and U.S. Pat. No. 5,299,081 issued to Hatch et al. on Mar. 29, 1994.
Use of dampers in head suspension design and construction typically involves use of a damping material, such as visco-elastic material, overlaying a portion of the load beam. Visco-elastic materials can expand and compress at a free surface thereof. However, greater energy can be dissipated by the damping material, achieving greater damping, if the free surface of the damping material is not allowed to expand and compress and the damping material is forced to shear. Accordingly, greater damping can be achieved by constraining the free surface of the damper with a relatively rigid constraint layer.
Constraint layers are often formed from stainless steel or other rigid material. For example, Blaeser discloses a head suspension having a load beam formed of a top constraint layer of stainless steel, a middle layer of damping material and a lower constraint layer of stainless steel. The entirety of the load beam, including the rigid region, spring or radius region and base or mounting region, has this laminated construction. In one embodiment of Blaeser, the flexure and the lower constraint layer are formed from a single sheet of stainless steel. This has the advantage of mitigating some of the difficulties of alignment of the flexure and/or the lower constraint layer when they are integrated with the remainder of the head suspension in assembly because they can both be aligned and attached at the same time.
However, making the flexure and the lower constraint layer together as one piece of the load beam can cause excessive transfer of resonance vibrations from the constraint layer to the flexure through the coupling region. Further, the radius region of the load beam primarily controls the spring characteristics of the load beam such as gram load (the force in the direction of the disk which the load beam places on the head slider) and spring rate (roughly, the stiffness of the radius region). As such, extending the laminated structure completely through the spring region and onto the base can adversely impact the spring characteristics of the radius region. Moreover, attaching the flexure to the load beam only via the flexure's connection to the lower constraint layer of the damper, rather than also attaching the flexure directly to the load beam, can also increase vibration in the flexure because there are fewer attachment points to stabilize the flexure.
Accordingly, there is a continuing need for improved damping of head suspensions. In particular, transfer of vibration of the load beam to the flexure should be reduced. Also, the spring characteristics of the load beam should be effected as little as possible by the damping. Additionally, the damped suspension should be reliable and capable of being efficiently manufactured.